OpenVR Support

added Feature label

added Doing label and removed Feature label

Mostly working, only need to correct the eye pose matrices and allow a GUI option to not use a VR headset if one is plugged in. Next step is to allow the user to walk and used the hand held devices to move around the scene more.

added To Do label and removed Doing label

added Doing label and removed To Do label

assigned to @joseha

mentioned in merge request !138 (merged)

closed via merge request !138 (merged)